THE EDITOR, Sir:
THE SCIENTIFIC Research Council of Jamaica should be commended for last Thursday night's panel discussion of some soil problems in Jamaica. However, as one of the panellists, I did wish to dispel a misconception voiced by a few members of the audience, and which were neither fully addressed or clarified by the panel.
It was claimed that the practice of monoculture and burning the sugar estate lands "every year for 200 years" is responsible for soil production problems. However, it is important to ascertain the kind of burning practised in the past and at present on the sugar estates before speculating on its effects. There is a difference between this type of burning and that practised for land clearing.
In the latter case, the woody native vegetation is set alight, generating very high temperatures (due to the large mass of solid wood involved). Tropical forest structure is the most complex of all biomes, consisting of at least three, often four tiers (height levels) of vegetation and, therefore, the largest mass of photosynthate in the world. Temperatures attained during the conflagration involving such closely packed, massive trees are sometimes high enough to melt glass. Even below the surface, molten organic gums in such fires seal off soil pores, thus severely restricting water movements within and below rooting zones. Eventually, this leads to topsoil erosion by running water due to the reduced infiltration acquired during the burning of organic soil-binding cements.
Therefore, it is not surprising that in the humid tropics, wherever burning is practised for land clearing, the land, though highly productive in the first two or three years after burning, soon becomes impoverished, then abandoned for a new forested area. Hence the use of the term "shifting cultivation".
What of the burning practices on sugar estate land? First of all, the above-ground biomass here is substantially less than that in the previous case. In fact, the canes themselves, it goes without saying, are never burnt in the process. The intention here is to get rid of the leaves, some distance above the ground, to facilitate harvesting. Thus for the above reasons, the soil cannot be damaged as much. Had such destruction occurred, the sugar estate lands could not have lasted as long as even 10 years without the need for 'shifting', let alone 200 years up to the present time. Since none of the Jamaican sugar estates have been perpetually 'shifting' to other locations in all that time, 'land burning' cannot be a full and satisfactory explanation for a lack of soil productivity on such lands.
I am, etc.,
MARK HARRIS
Environmental geoscientist
Northern Caribbean University
